Vertically aligned nanowire channels with source/drain interconnects for nanosheet transistors

ABSTRACT

A nano-sheet semiconductor structure and a method for fabricating the same. The nano-sheet structure includes a substrate and at least one alternating stack of semiconductor material layers and metal gate material layers. The nano-sheet semiconductor structure further comprises a source region and a drain region. A first plurality of epitaxially grown interconnects contacts the source region and the semiconductor layers in the alternating stack. A second plurality of epitaxially grown interconnects contacts the drain region and the semiconductor layers in the alternating stack. The method includes removing a portion of alternating semiconductor layers and metal gate material layers. A first plurality of interconnects is epitaxially grown between and in contact with the semiconductor layers and the source region. A second plurality of interconnects is epitaxially grown between and in contact with the semiconductor layers and the drain region.

BACKGROUND OF THE INVENTION

The present invention generally relates to the field of semiconductors,and more particularly relates to nanowire field-effect-transistors.

Nanowire field-effect-transistor (FET) devices include a nanowirearranged on a substrate. A gate stack is arranged conformally on achannel region of the nanowire. Source and drain regions of the nanowireextend outwardly from the channel region.

As the size of semiconductor devices decreases, it has become desirableto increase the density of the arrangement of FET devices on asubstrate.

SUMMARY OF THE INVENTION

In one embodiment, a method for fabricating a semiconductor structure isprovided. The method includes forming a structure including at least analternating stack of semiconductor layers with variablespacing/thicknesses and metallic gates formed on a substrate. The metalgate is formed on and in contact with a top layer of the alternatingstack, a source region and a drain region in contact with thesemiconductor layers of the alternating stack, and dielectric layersformed on and in contact with a top surface of the source and drainregions, respectively. The method includes depositing a dielectricspacer to protect areas the semiconductor layers and metal gate whileremoving regions left exposed. The removal process forms a trenchexposing sidewalls of the metal gate and sidewalls of the source anddrain regions. A first plurality of interconnects is epitaxially grownbetween and in contact with the semiconductor layers and the sourceregion. A second plurality of interconnects is epitaxially grown betweenand in contact with the semiconductor layers and the drain region.

In another embodiment, a semiconductor structure is provided. Thesemiconductor structure includes a substrate and at least onealternating stack of semiconductor material layers and metal gatematerial layers disposed on the substrate. A metal gate is disposed onand in contact with the alternating stack of semiconductor materiallayers and metal gate material layers. The semiconductor structurefurther comprises a source region and a drain region. A first pluralityof epitaxially grown interconnects contacts the source region and thesemiconductor layers in the alternating stack. A second plurality ofepitaxially grown interconnects contacts the drain region and thesemiconductor layers in the alternating stack.

In yet another embodiment, an integrated circuit is provided. Theintegrated circuit includes a semiconductor structure. The semiconductorstructure includes a substrate and at least one alternating stack ofsemiconductor material layers and metal gate material layers disposed onthe substrate. A metal gate is disposed on and in contact with thealternating stack of semiconductor material layers and metal gatematerial layers. The semiconductor structure further comprises a sourceregion and a drain region. A first plurality of epitaxially growninterconnects contacts the source region and the semiconductor layers inthe alternating stack. A second plurality of epitaxially growninterconnects contacts the drain region and the semiconductor layers inthe alternating stack

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying figures where like reference numerals refer toidentical or functionally similar elements throughout the separateviews, and which together with the detailed description below areincorporated in and form part of the specification, serve to furtherillustrate various embodiments and to explain various principles andadvantages all in accordance with the present invention, in which:

FIG. 1 is a cross-sectional view of an initial nano-sheet semiconductorstructure comprising an alternating stack of first and secondsemiconductor layers according to one embodiment of the presentinvention;

FIG. 2A is a top-down view of the nano-sheet semiconductor structureafter disposable gates and their spacers have been formed thereonaccording to one embodiment of the present invention;

FIG. 2B is a cross-sectional view of the nano-sheet semiconductorstructure taken along line B-B′ shown in FIG. 2A after disposable gatesand their spacers have been formed thereon according to one embodimentof the present invention;

FIG. 2C is a cross-sectional view of the nano-sheet semiconductorstructure taken along line C-C′ shown in FIG. 2A after disposable gatesand their spacers have been formed thereon according to one embodimentof the present invention;

FIG. 3 is a cross-sectional view of the nano-sheet semiconductorstructure after portions the nano-sheet have been removed according toone embodiment of the present invention;

FIG. 4 is a cross-sectional view of the nano-sheet semiconductorstructure after source and drain regions have been formed according toone embodiment of the present invention;

FIG. 5 is a cross-sectional view of the nano-sheet semiconductorstructure after an inter-layer dielectric layer has been formed on thesource and drain regions according to one embodiment of the presentinvention;

FIG. 6 is a cross-sectional view of the nano-sheet semiconductorstructure after the disposable gates have been removed according to oneembodiment of the present invention;

FIG. 7 is a cross-sectional view of the nano-sheet semiconductorstructure after the first semiconductor layers have been removedaccording to one embodiment of the present invention;

FIG. 8 is a cross-sectional view of the nano-sheet semiconductorstructure after a metal gate material has been deposited to form a metalgate on a top-most layer of the second semiconductor layers, and to formmetal gate material layers in the areas where the first semiconductorlayers have been removed according to one embodiment of the presentinvention;

FIG. 9 is a cross-sectional view of the nano-sheet semiconductorstructure after a cap layer has been formed on the metal gates accordingto one embodiment of the present invention;

FIG. 10 is a cross-sectional view of the nano-sheet semiconductorstructure after the spacers have been removed forming trenches adjacentto the inter-layer dielectric layers according to one embodiment of thepresent invention;

FIG. 11 is a cross-sectional view of the nano-sheet semiconductorstructure after portions of the alternating second semiconductor layersand metal gate material layers underlying the trenches of FIG. 10 havebeen removed according to one embodiment of the present invention;

FIG. 12 is a cross-sectional view of the nano-sheet semiconductorstructure after interconnects have been epitaxially grown between and incontact with the second semiconductor layers and the source/drainregions according to one embodiment of the present invention;

FIG. 13 is a cross-sectional view of the nano-sheet semiconductorstructure after a spacer material has been deposited within the trenchesin contact with the top-most interconnects, the inter-layer dielectriclayers, and the metal gates according to one embodiment of the presentinvention; and

FIG. 14 is an operational flow diagram illustrating one process forfabricating nano-sheet semiconductor structures according to oneembodiment of the present invention.

DETAILED DESCRIPTION

It is to be understood that the present invention will be described interms of a given illustrative architecture; however, otherarchitectures, structures, substrate materials and process features andsteps may be varied within the scope of the present invention.

It will also be understood that when an element such as a layer, regionor substrate is referred to as being “on” or “over” another element, itcan be directly on the other element or intervening elements may also bepresent. In contrast, when an element is referred to as being “directlyon” or “directly over” another element, there are no interveningelements present. It will also be understood that when an element isreferred to as being “connected” or “coupled” to another element, it canbe directly connected or coupled to the other element or interveningelements may be present. In contrast, when an element is referred to asbeing “directly connected” or “directly coupled” to another element,there are no intervening elements present.

One or more embodiments include a design for an integrated circuit chip,which is created in a graphical computer programming language, andstored in a computer storage medium (such as a disk, tape, physical harddrive, or virtual hard drive such as in a storage access network). Ifthe designer does not fabricate chips or the photolithographic masksused to fabricate chips, the designer is able to transmit the resultingdesign by physical means (e.g., by providing a copy of the storagemedium storing the design) or electronically (e.g., through theInternet) to such entities, directly or indirectly. The stored design isthen converted into the appropriate format (e.g., GDSII) for thefabrication of photolithographic masks, which typically include multiplecopies of the chip design in question that are to be formed on a wafer.The photolithographic masks are utilized to define areas of the wafer(and/or the layers thereon) to be etched or otherwise processed.

Methods as described herein are utilized in the fabrication ofintegrated circuit chips. The resulting integrated circuit chips aredistributable by the fabricator in raw wafer form (that is, as a singlewafer that has multiple unpackaged chips), as a bare die, or in apackaged form. In the latter case the chip is mounted in a single chippackage (such as a plastic carrier, with leads that are affixed to amotherboard or other higher-level carrier) or in a multichip package(such as a ceramic carrier that has either or both surfaceinterconnections or buried interconnections). In any case, the chip isthen integrated with other chips, discrete circuit elements, and/orother signal processing devices as part of either (a) an intermediateproduct, such as a motherboard, or (b) an end product. The end productcan be any product that includes integrated circuit chips, ranging fromtoys and other low-end applications to advanced computer products havinga display, a keyboard or other input device, and a central processor.

Reference in the specification to “one embodiment” or “an embodiment” ofthe present principles, as well as other variations thereof, means thata particular feature, structure, characteristic, and so forth describedin connection with the embodiment is included in at least one embodimentof the present principles. Thus, the appearances of the phrase “in oneembodiment” or “in an embodiment”, as well any other variations,appearing in various places throughout the specification are notnecessarily all referring to the same embodiment.

Referring now to the drawings in which like numerals represent the sameof similar elements, FIGS. 1-13 illustrate various processes forfabricating nano-sheet FETs having vertically alignednano-sheet/nanowire channels and source/drain interconnects. FIG. 1illustrates one example of a semiconductor structure 100 that includes ahandle substrate 102, and a stack of alternating first semiconductormaterial and a second semiconductor material. The handle substrate 102,in one embodiment, includes a semiconductor material, an insulatormaterial, a conductive material, or a combination thereof. The thicknessof the handle substrate 102, in one embodiment, ranges from 50 micronsto 2 mm, although lesser and greater thicknesses can also be employed.

The stack includes at least one first semiconductor material layer 106and at least one second semiconductor material layer 108. In oneembodiment, the stack can include a plurality of first semiconductormaterial layers 106 and a plurality of second semiconductor materiallayers 108. As used herein, a “semiconductor material” refers to amaterial having a conductivity in a range from 3.0×10⁻⁴ Ohm-cm to3.0×10³ Ohm-cm, and includes an intrinsic semiconductor material, ap-doped semiconductor material, an n-doped semiconductor material, or acombination of semiconductor materials having different types of doping.The first semiconductor material layers 106 include a firstsemiconductor material that can be removed selective to the secondsemiconductor material of the second semiconductor material layers 108.Each of the at least one first semiconductor material layers 106 and thesecond semiconductor material layers 108 can be single crystalline. Inone embodiment, the entirety of the stack (106, 108) is singlecrystalline

In one embodiment, the first semiconductor material layers 106 include asilicon-containing semiconductor material in which the atomicconcentration of silicon is greater than 80%, and the secondsemiconductor material layers 108 include a germanium-containingsemiconductor material in which the atomic concentration of germanium isgreater than 20%. For example, the first semiconductor material layers106 can include single crystalline silicon or a single crystallinesilicon-germanium alloy in which the atomic concentration of germaniumis less than 20%.

In another embodiment, the first semiconductor material layers 106include a first single crystalline compound semiconductor material, andthe second semiconductor material layers 108 include a second singlecrystalline compound semiconductor material that can be removedselective to the first single crystalline compound semiconductormaterial. For example, the first semiconductor material layers 108include In—Ga_(1-x)As, GaAs, or InP, and the second semiconductormaterial layers 108 include GaP or GaN. In one embodiment, each of thefirst semiconductor material layers 106 is deposited as a singlecrystalline semiconductor material layer in epitaxial alignment with anunderlying material layer. In one embodiment, each of the secondsemiconductor material layers 108 is deposited as a single crystallinematerial layer in epitaxial alignment with an underlying material layer.

The thicknesses of the first semiconductor material layers 106 and thesecond semiconductor material layers 108 are selected such that theentirety of the epitaxial alignment of the first semiconductor materiallayers 106 and the second semiconductor material layers 108 can bemaintained throughout the entirety of the stack. Thus, the thickness ofeach of the first semiconductor material layers 106 and the secondsemiconductor material layers 108 is less than the correspondingcritical thickness, which is the thickness at which an epitaxialmaterial begins to lose epitaxial registry with the underlying singlecrystalline layer by developing dislocations. For example, the thicknessof each of the first semiconductor material layers 106 and the secondsemiconductor material layers 108 is in a range from 3 nm to 60 nm,although lesser and greater thicknesses can also be employed.

In some embodiments, the stack (106, 108) is formed by a series ofepitaxial growth processes. The terms “epitaxial growth”, “epitaxialdeposition”, “epitaxially formed”, epitaxially grown“, and theirvariants and/or grown” mean the growth of a semiconductor material on adeposition surface of a semiconductor material, in which thesemiconductor material being grown has the same crystallinecharacteristics as the semiconductor material of the deposition surface.In an epitaxial deposition process, the chemical reactants provided bythe source gases are controlled and the system parameters are set sothat the depositing atoms arrive at the deposition surface of thesemiconductor substrate with sufficient energy to move around on thesurface and orient themselves to the crystal arrangement of the atoms ofthe deposition surface. Therefore, an epitaxial semiconductor materialhas the same crystalline characteristics as the deposition surface onwhich it is formed. For example, an epitaxial semiconductor materialdeposited on a {100} crystal surface will take on a {100} orientation.In some embodiments, epitaxial growth and/or deposition processes areselective to forming on semiconductor surface, and do not depositmaterial on dielectric surfaces, such as silicon dioxide or siliconnitride surfaces.

In one embodiment, the number of repetitions for a pair of a firstsemiconductor material layer 106 and a second semiconductor materiallayer 108 is 2 or greater. In one embodiment, the number of repetitionsfor a pair of a first semiconductor material layer 106 and a secondsemiconductor material layer 108 is in a range from, and including, 2to, and including, 100. The stack (106, 108), in one embodiment, begins,at the bottom, with a first semiconductor material layer 106 or with asecond semiconductor material layer 108. In one embodiment, the stackterminates, at the top, with a first semiconductor material layer 106 orwith a second semiconductor material layer 108.

An optional cap material layer (not shown) can be formed on top of thestack (106, 108). The cap material layer, in one embodiment, includes adielectric material such as silicon nitride, silica oxide or adielectric metal oxide, and can be formed by chemical vapor deposition(CVD). The thickness of the cap material layer, in one embodiment,ranges from 3 nm to 60 nm, although lesser and greater thicknesses canalso be employed. The stack (106, 108) of the first semiconductormaterial layers 106 and the second semiconductor material layers 108 arepatterned to form the one or more alternating vertical stacks 110 ofalternating first and second semiconductor material layers 106, 108, asshown in FIG. 1.

For example, a photoresist layer (not shown) can be applied over the topsecond semiconductor material layer 108 (or the optional cap layer ifformed) and lithographically patterned to cover a contiguous area. Theshape of the contiguous area covered by the patterned photoresist layercan be selected to include an elongated region having a same width andtwo end portions having a greater width than the elongated region. Thepattern in the photoresist layer can be transferred through thealternating stack by an anisotropic etch. A remaining portion of thestack of the first semiconductor material layers 106 and the secondsemiconductor material layers 108 constitute the alternating stack 110of the first semiconductor material portions 106 and the secondsemiconductor material portions 108. In one embodiment, the entirety ofthe alternating stack 110 can be single crystalline. Besides thelithography patterning, other patterning techniques such as sidewallimaging transfer, multiple patterning, or the combination of thosetechniques can be used to pattern the stack.

In one embodiment, each of the first semiconductor material portions 106and the second semiconductor material portions 108 has a uniform widthin a range from 10 nm to 100 nm. The first semiconductor materialportions 106 and the second semiconductor material portions 108, in oneembodiment, have sidewalls that are vertically coincident among oneanother. As used herein, surfaces are “vertically coincident” if thesurfaces are located within a same vertical plane. In one embodiment,first semiconductor material portions 106 and the second semiconductormaterial portions 108 have a same horizontal cross-sectional shape. Inone embodiment, first semiconductor material portions 106 and the secondsemiconductor material portions 108 are semiconductor material fins andsecond semiconductor material fins, respectively. As used herein, a“fin” refers to a structure having a pair of vertical sidewalks and auniform width between the pair of vertical sidewalk that is invariantunder translation along the direction of the vertical sidewalls. Thealternating stack 110 of the first semiconductor material portions 106and the second semiconductor material portions 108 constitutes asemiconductor fin having a pair of parallel sidewalk that extend along alengthwise direction and having a uniform width throughout. As usedherein, a “lengthwise direction” is a horizontal direction around whichan axis passing through a center of mass of an element would have theleast moment of inertia.

In one embodiment, the first semiconductor material portions 106 and thesecond semiconductor material portions 108 are single crystalline andepitaxially aligned among one another. Further, the first semiconductormaterial portions 106 and the second semiconductor material portions108, in on embodiment, have different lattice constants. In this case,the first semiconductor material portions 106 and the secondsemiconductor material portions 108 can be in opposite types of stressalong horizontal directions. If the optional cap layer is employed, itcan be removed once the alternating stack 110 of the first semiconductormaterial portions 106 and the second semiconductor material portions 108is formed, for example, by a wet etch that removes the material of thecap layer selective to the substrate 102 and the alternating stack 110of the first semiconductor material portions 106 and the secondsemiconductor material portions 108.

FIGS. 2A-2C show that one or more disposable gate structures 201, 203,205 are formed over and across (wrapping) the alternating stack 110 ofthe first semiconductor material portions 106 and the secondsemiconductor material portions 108. FIG. 2A shows a top-down view ofthe structure 100, whereas FIGS. 2B and 2C are cross-sections takenalong lines B-B′ and C-C′, respectively, shown in FIG. 2A. In oneembodiment, each of the disposable gate structures 201, 203, 205includes a disposable gate portion 202, 204, 206 and a disposable gatecap 208, 210, 212. In one embodiment, the disposable gate portions 202,204, 206 include a dielectric material. For example, the disposable gateportions 202, 204, 206 include amorphous carbon, diamond-like carbon(DLC), a dielectric metal oxide, silicon nitride, or an organosilicateglass. Alternatively, the disposable gate portions 202, 204, 206 includea stack of a disposable material liner (not shown) and a disposable gatematerial portion (not shown). In this case, the disposable materialliner can include a dielectric material such as silicon oxide. Thedisposable gate material portion, in one embodiment, includes adielectric material, a semiconductor material, or a conductive material,provided that the disposable gate material portion can be removedselective to the dielectric materials of a planarization dielectriclayer and a gate spacer to be subsequently formed. The disposable gatecaps 208, 210, 212, include a material such as silicon nitride.

The disposable gate structures 201, 203, 205, in one embodiment, areformed by deposition and patterning of at least one material layer. Thepatterning of the at least one material layer can be performed by acombination of lithographic methods and an anisotropic etch. Thedisposable gate structures 201, 203, 205 straddle, and contacts sidewalkof, the alternating stack 110 of the first semiconductor materialportions 106 and the second semiconductor material portions 108.

FIG. 2 further shows that a gate spacer 214, 216, 218 is formed around(wraps) each of the disposable gate structure 201, 203, 205. In oneembodiment, the gate spacers 214, 216, 218, are formed by depositing aconformal dielectric material layer on the disposable gate structures201, 203, 205 and the alternating stack 110 of the first semiconductormaterial portions 106 and the second semiconductor material portions108, and anisotropically etching the conformal dielectric materiallayer. The conformal dielectric material layer includes a dielectricmaterial that is different from the material of the disposable gateportions 202, 204, 206. For example, the conformal dielectric materiallayer can include silicon nitride, silicon oxide, and/or dielectricmetal oxide. An anisotropic etch process is employed to anisotropicallyetch horizontal portions of the conformal dielectric material layer.Further, vertical portions of the conformal dielectric material layerare recessed below a top surface of the disposable gate caps 208, 210,212.

FIG. 3 shows that exposed portions of the alternating stack 110, whichdo not underlie a disposable gate stack and spacer 214, 216, 218, areremoved. For example, a directional etching process such as areactive-ion-etching (RIE) process is utilized to remove the exposedportions of the alternating stack 110. This etching process results in atrench 302, 304 being formed between the spacers 214, 216, 218 ofneighboring disposable gate stacks 202, 204, 206. Each of the trenchesexpose a portion of the substrates top surface 306, 308; ends 310, 312,314 of the first semiconductor material portions 106; and ends 316, 318,320 of the second semiconductor material portions 108. It should benoted that FIG. 3 shows the ends 310, 312, 314 of the firstsemiconductor material portions 106 and ends 316, 318, 320 of the secondsemiconductor material portions 108 extending past the spacers sidewallsfor illustration purposes only.

A selective epitaxy process is then performed to form source and drainregions 402, 404 as shown in FIG. 4. In one embodiment, the ends 310,312, 314 of the first semiconductor material portions 106 and/or theends 316, 318, 320 of the second semiconductor material portions 108 areused as seeds for the epitaxy process. During the selective epitaxyprocess, a semiconductor material is deposited only on semiconductorsurfaces, and does not nucleate on dielectric surfaces. The sourceregion 402 grows from surfaces of the first semiconductor materialportions 106 and/or the second semiconductor material portions 108located on one side of the disposable gate structures 201, 203, 205. Thedrain region 404 grows from surfaces of the first semiconductor materialportions 106 and/or the second semiconductor material portions 108located on the other side of the disposable gate structures 201, 203,205. Each of the source and drain regions 402, 404, in one embodiment issingle crystalline, and is epitaxially aligned to the single crystallinestructure of the vertical stack of the first semiconductor materialportions 106 and the second semiconductor material portions 108. Thesource and drain regions 402, 404, in one embodiment, is formed within-situ doping of the electrical dopants, or by deposition of anintrinsic semiconductor material and subsequent introduction ofelectrical dopants by ion implantation, plasma doping, gas phase doping,or out-diffusion from a disposable doped silicate glass layer. In oneembodiment, activation of the dopants forms a sharp junction.

FIG. 5 shows that the trenches 302, 304 are filled with an inter-layerdielectric (ILD) 502, 504 after the source and drain regions 402, 404have been formed. A chemical mechanical planarization (CMP) is thenperformed. The CMP process stops at a top surface of the spacers 214,216, 218. The interlayer dielectric 502, 504, in one embodiment,comprises SiO2, Si3N4, SiOxNy, SiC, SiCO, SiCOH, and SiCH compounds; oneor more silicon-based materials with some or all of the Si replaced byGe; carbon-doped oxides; inorganic oxides; inorganic polymers; hybridpolymers; organic polymers such as polyamides or SiLK™; othercarbon-base materials; organo-inorganic materials such as spin-onglasses and silsesquioxane-based materials; and diamond-like carbon(DLC, also known as amorphous hydrogenated carbon, α-C:H). Additionalchoices for the interlayer dielectric 502, 504 include any of theaforementioned materials in porous form, or in a form that changesduring processing to or from being porous and/or permeable to beingnon-porous and/or non-permeable.

The disposable gate structures 201, 203, 205 are then removed, as shownin FIG. 6. At least one etch process, which can include an isotropicetch and/or an anisotropic etch, is utilized to remove the disposablegate structures 201, 203, 205. For example, the disposable gatestructures 201, 203, 205 can be removed by wet etch processes. A gatecavity 602, 604, 606 is formed in the volume from which the disposablegate structures 201, 203, 205. A portion 608, 610, 612 of the topsurface of the top/upper most second semiconductor portion 108 isexposed within each gate cavity 602, 604, 606. Sidewall surfaces of aportion of the spacers 214, 216, 218 are also exposed within each gatecavity 602, 604, 606.

FIG. 7 shows that a selective etching process is performed to remove thefirst semiconductor material portions 106 selective to the secondsemiconductor material portions 108 of the alternating stack 110. Forexample, a wet etch process or a reactive ion etch process can beutilized to selectively remove the first semiconductor material portions106 of the alternating stack 110. This process forms cavities 702, 704,706 between each of the second semiconductor material portions 108 ofthe alternating stack 110, which are anchored by the epitaxy material ofthe source/drain regions 402, 404.

A replacement gate structure 802, 804, 806 is formed within each of thegate cavities 602, 604, 606, as shown in FIG. 8. For example, at leastone conductive material is deposited to form at least one conductivematerial layer within the each of the gate cavities 602, 604, 606 andwithin each of the cavities 702, 704, 706 between each of the secondsemiconductor material portions 108 of the alternating stack 110. Then,any conductive material layer above the top surface of the spacers 214,216, 218 and ILD 502, 504 is removed, for example, by chemicalmechanical planarization (CMP). The remaining portion of the at leastone conductive material layer constitutes the replacement gate structure802, 804, 806 with replacement gate material disposed between each ofthe second semiconductor material portions. Therefore, the alternatingstack 110 now comprises alternating layers of metal gate material layers808, 810, 812 and second semiconductor material portions layers 108.

The replacement gate structures 802, 804, 806 are then recessed to forma cap layer 902, 904, 906, as shown in FIG. 9. The cap layers 902, 904,906, in one embodiment, comprise a dielectric material such as siliconnitride, silicon oxide, or a dielectric metal oxide formed by chemicalvapor deposition (CVD) or any other suitable method. Any cap layermaterial above the top surface of the spacers 214, 216, 218 and the MDlayers 502, 504 is removed.

One issue with the structure shown in FIG. 9 is that the replacementgate structure 802, 804, 806 can short to the source/drain 402, 404since the gate metal fills in spaces close to the material of thesource/drain 402, 404. This can result in poor capacitance. Therefore,after the cap layers 902, 904, 906 are formed the spacers 214, 216, 218are removed, as shown in FIG. 10. For example, an anisotropic etch withlow selectivity to Si/SiGe is performed to remove both the spacer andnanowires simultaneously. This process forms a trench 1002, 1004, 1006,1008 between the sidewalls of the gate structures 802, 804, 806(including their cap layers 902, 904, 906) and the ILD layers 502, 504.The trenches 1002, 1004, 1006, 1008 expose a portion of the top surfaceof the top/upper most second semiconductor portion 108.

An isotropic RIE process is then performed to remove the materialunderlying the underlying the trenches 1002, 1004, 1006, 1008, as shownin FIG. 11. For example, the portions of the second semiconductormaterial 108 and the portions of the metal gate material 802 betweeneach layer of the second semiconductor material 108 underlying thetrenches 1002, 1004, 1006, 1008 is removed. This etching process extendsthe trenches 1002, 1004, 1006, 1008 down to (and exposing) the topsurface of substrate 102.

A material is then epitaxially grown between and contacting each exposedportion of the second semiconductor material 108 and the source/drains402, 404 within the trenches 1002, 1004, 1006, 1008, as shown in FIG.12. The epitaxially grown material, in on embodiment, is a semiconductormaterial such as (but not limited to) Si, SiGe, with various levels ofGe, and stress/strain as well as options for additional doping of B, P.The material, in one embodiment, is formed with in-situ doping of theelectrical dopants. The grown material forms interconnects 1202, 1204,1206, 1208 ends/sidewalls of the second semiconductor material 108exposed within the trenches 1002, 1004, 1006, 1008 and sidewalls of thesource/drain regions 402, 404.

The epitaxial growth process also forms air gaps (pockets/cavities)1210, 1212, 1214 between vertical pairs of interconnects and between thetop surface of the substrate 102 and the interconnect directly above thesubstrate 102. The air gaps (pockets/cavities) 1210, 1212, 1214 act asspacers between the interconnects 1202, 1204, 1206, 1208 and the gatemetal material layers 808, 810, 812. FIG. 13 shows that portions of thetrenches 1002, 1004, 1006, 1008 remaining above the uppermostinterconnects 1202, 1204, 1206, 1208 are backfilled with a spacermaterial to form spacers 1302, 1304, 1306, 1308, therein. The spacermaterial, in one embodiment, comprises a dielectric material such asSiN, SiBCN, SiBCO or other low-k materials. The structure shown in FIG.13 provides controllable low-level leakage from the gate to source drainregions. In addition, additional control over the interconnect materialprovides improved performance/speed of devices.

FIG. 14 is an operational flow diagram illustrating one process forfabricating a nano-sheet semiconductor structure. It should be notedthat each of the steps shown in FIG. 14 has been discussed in greaterdetail above with respect to FIGS. 1-13. In FIG. 14, the operationalflow diagram begins at step 1402 and flows directly to step 1404. Astructure, at step 1404, is formed including at least an alternatingstack of semiconductor layers and metal gate material layers formed on asubstrate, a metal gate formed on and in contact with a top layer of thealternating stack, a source region and a drain region in contact withthe semiconductor layers of the alternating stack, and dielectric layersformed on and in contact with a top surface of the source and drainregions, respectively.

A portion of the semiconductor layers and metal gate material layers, isremoved, at step 1406. This removal process forms a trench exposingsidewalls of the metal gate and sidewalls of the source and drainregions. A first plurality of interconnects, at step 1408, isepitaxially grown between and in contact with the semiconductor layersand the source region. A second plurality of interconnects, at step1410, is epitaxially grown between and in contact with the semiconductorlayers and the drain region. The control flow exits at step 1412

Although specific embodiments of the invention have been disclosed,those having ordinary skill in the art will understand that changes canbe made to the specific embodiments without departing from the spiritand scope of the invention. The scope of the invention is not to berestricted to the specific embodiments, and it is intended that theappended claims cover any and all such applications, modifications, andembodiments within the scope of the present invention.

It should be noted that some features of the present invention can beused in one embodiment thereof without use of other features of thepresent invention. As such, the foregoing description should beconsidered as merely illustrative of the principles, teachings,examples, and exemplary embodiments of the present invention, and not alimitation thereof.

Also, these embodiments are only examples of the many advantageous usesof the innovative teachings herein. In general, statements made in thespecification of the present application do not necessarily limit any ofthe various claimed inventions. Moreover, some statements may apply tosome inventive features but not to others.

What is claimed is:
 1. A method for forming a semiconductor structure,the method comprising: forming a structure comprising at least analternating stack of semiconductor layers and metal gate material layersformed on a substrate, a metal gate formed on and in contact with a toplayer of the alternating stack, a source region and a drain region incontact with the alternating stack, and dielectric layers formed on andin contact with a top surface of the source and drain regions,respectively; removing a portion of the semiconductor layers and metalgate material layers, wherein the removing forms trenches exposing atleast sidewalls of the source and drain regions; forming a firstplurality of interconnects between and in contact with the semiconductorlayers and the source region; and forming a second plurality ofinterconnects between and in contact with the semiconductor layers andthe drain region.
 2. The method of claim 1, further comprising: prior toremoving the portion of the semiconductor layers and metal gate materiallayers, etching spacers surrounding the source region, the drain region,and the dielectric layers, wherein the etching forms trenches betweenthe metal gate and the dielectric layers and above the portion of thesemiconductor layers and metal gate material layers.
 3. The method ofclaim 2, further comprising: after the first and second plurality ofinterconnects have been formed, depositing a spacer material within thetrenches.
 4. The method of claim 1, wherein forming the first and secondplurality of interconnects forms air pockets between the metal gatematerial layers and the source region, and between the metal gatematerial layers and the drain region.
 5. The method of claim 1, whereinforming the structure comprises: forming an alternating vertical stackof the semiconductor layers and sacrificial semiconductor layers;forming at least one disposable gate on the alternating vertical stack;and forming a spacer around the disposable gate and a portion of thealternating vertical stack underlying the disposable gate.
 6. The methodof claim 5, further comprising: forming a cap layer on and in contactwith a top portion of the alternating stack of semiconductor layers. 7.The method of claim 5, wherein forming the structure comprises:epitaxially growing each semiconductor layer and each sacrificialsemiconductor layer in the alternating stack of semiconductor layers andsacrificial semiconductor layers.
 8. The method of claim 7, wherein theforming further comprises: patterning the alternating stack ofsemiconductor layers and sacrificial semiconductor layers.
 9. The methodof claim 5, wherein forming the structure further comprises: removingthe disposable gate, the removing forming a trench exposing the portionof the alternating vertical stack; and removing the sacrificialsemiconductor layers.
 10. The method of claim 9, wherein forming thestructure further comprises depositing metal gate material within thetrench, wherein the depositing forms the metal gate and the metal gatematerial layers.
 11. The method of claim 5, wherein forming thestructure further comprises: removing a first portion of the alternatingvertical stack in a first area corresponding to the source region;removing a second portion of the alternating vertical stack in a secondarea corresponding to the drain region; and epitaxially growing thesource region and the drain region within the first and second areas,respectively, wherein the source and drain regions are grown in contactwith the portion of the alternating vertical stack underlying thedisposable gate.
 12. The method of claim 11, further comprising:depositing an inter-layer dielectric material on and in contact with thesource region and the drain region.
 13. The method of claim 1, furthercomprising: forming a cap layer on and in contact with the metal gate.14. A method for forming a semiconductor structure, the methodcomprising: forming an alternating stack of semiconductor layers andmetal gate material layers on a substrate; forming a metal gate on andin contact with a top layer of the alternating stack; removing a portionof the semiconductor layers and metal gate material layers, wherein theremoving forms at least one trench; and forming a plurality ofinterconnects within the at least one trench, wherein each interconnectin plurality of interconnects contacts a semiconductor layer of thealternating stack, the formation of the plurality of interconnects formsair pockets between pairs of interconnects in the plurality ofinterconnects.
 15. The method of claim 14, further comprising: after theplurality of interconnects have been formed, depositing a spacermaterial within the first and second trenches.
 16. The method of claim14, wherein forming alternating stack of semiconductor layers and metalgate material layers comprises: forming an alternating vertical stack ofthe semiconductor layers and sacrificial semiconductor layers.
 17. Themethod of claim 16, further comprising: patterning the alternatingvertical stack of semiconductor layers and sacrificial semiconductorlayers.
 18. The method of claim 16, further comprising: removing thesacrificial semiconductor layers, the removing forming voids between thesemiconductor layers; and depositing metal gate material within thevoids, wherein the depositing forms the metal gate material layers. 19.The method of claim 14, wherein forming the metal gate comprises:forming an alternating vertical stack of the semiconductor layers andsacrificial semiconductor layers; forming at least one disposable gateon the alternating vertical stack; forming a spacer around thedisposable gate and a portion of the alternating vertical stackunderlying the disposable gate; after forming the spacer, removing thedisposable gate, the removing forming a trench exposing the portion ofthe alternating vertical stack; removing the sacrificial semiconductorlayers; and depositing metal gate material within the trench, whereinthe depositing forms the metal gate and the metal gate material layers.20. A method for forming a semiconductor structure, the methodcomprising: forming a structure comprising at least a plurality ofalternating stacks each comprising semiconductor layers and metal gatematerial layers formed on a substrate, and a plurality of doped regionseach in contact with at least one alternating stack of the plurality ofstacks; removing a portion of each alternating stack of the plurality ofstacks in contact with at least one doped region of the plurality ofdoped regions, the removing forming a plurality of trenches exposing asidewall of the at least one doped region; and epitaxially growing aplurality of interconnects within the trenches, wherein eachinterconnect of the plurality of interconnects is between and in contactwith one of the semiconductor layers and one doped region of theplurality of doped regions.